Customized Y-shaped Carbon Nanotubes Can Compute
“This is the first time that a transistor-like structure has been fabricated using a branched carbon nanotube,” said Bandaru. “This discovery represents a new way of thinking about nano-electronic devices, and I think people interested in creating functionality at the nanoscale will be inspired to explore the ramifications of these Y-junction elements in greater detail.”
“The small size and dramatic switching behavior of these nanotubes makes them candidates for a new class of transistor,” said Bandaru.
When electrical contacts are attached to the nanotube structures, electrons travel into one arm of the Y, hop onto the catalyst particle, and then hop to the other arm and flow outward. Experiments conducted in Bandaru’s lab at UCSD’s Jacobs School of Engineering showed that the movement of electrons through the Y-junction can be finely controlled, or gated, by applying a voltage to the stem. Bandaru hypothesized that positive charge applied to the stem enhances the flow of electrons through the two arms, producing a strong “on” signal. Then, when the polarity of the charge is reversed, the movement of electrons through the arms essentially stops, creating an “off” signal. Such binary logic is the basis of nearly all transistors.
“Among electrical device engineers, this phenomenon is called gating,” said Bandaru. He said the phenomenon effectively makes Y-shaped nanotubes the smallest ready-made transistor yet, with rapid switching speeds and possible three-way gating capability. In earlier attempts to make carbon nanotube-based transistors, separate gates were added rather than built in.
“We think this discovery extends the paradigm of nanotechnology beyond just making things small,” said Bandaru. “We can synthesize functionality at the nanoscale, in this case to include the three elements of a circuit – the gate, source, and drain – and we don’t have to go to the trouble of making them separately and assembling them.”
The researchers plan to experiment with various other catalyst particles in order to tailor the three-way gating properties of the Y-junctions. “If we can easily fabricate, manipulate, and assemble these nano-devices on a large scale they could become the basis of a new kind of transistor and nanotechnology,” said Bandaru.
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